Experimental evidence for a relationship between liquid immiscibility and ore-formation in felsic magmas |
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| Institution: | 1. Department of Pathology, Tianjin Medical University, Tianjin 300070, China;2. Department of Pathology, Tianjin Cancer Hospital, Tianjin Medical University, Tianjin 300060, China;3. Department of Pathology, Tianjin General Hospital, Tianjin Medical University, Tianjin 300052, China;4. Stomatology Hospital of Tianjin Medical University, Tianjin, China;5. Department of Pathology, Tianjin Hospital, Tianjin, China;1. Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan;2. Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1, Yamada-Oka, Suita, Osaka 565-0871, Japan;3. Technology Research Institute of Osaka Prefecture, 2-7-1, Ayumino, Izumi, Osaka 594-1157, Japan;4. Center for Supports to Research and Education Activities, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan |
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| Abstract: | Geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process. In order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma, we carried out a series of experiments at high temperature and atmospheric pressure. The experimental results show that the granite ∼ KBF4∼Na2MoO4 system is a homogeneous melt at high temperature. With decrease in temperature, however, the melt decomposes into two immiscible melts: silicate melt and ore-forming melt. The ore-forming melt exists as globules in the silicate phase. Molybdenm, Ca, Na, Mg, P, Mn, F, B, and OH are concentrated in these globules. The ore forming melt is characterized with very low SiO2 and Al2O3 concentrations but the concentration of MoO3 and CaO is very high. In contrast, the silicate melts are significantly enriched in SiO2 and Al2O3, and depleted in MoO3 and CaO. In the silicate melt the concentrations of network modifying elements (e.g. Mo, Ca, Na, P, Mg) and volatiles (F, OH) are very low. The differences between the two immiscible melts exist not only in chemical composition but also in structure. The ore-forming melt structurally consists of MoO4], MoOF4], B(OH)4], and OH, while the silicate melt is Si04]. Because of the difference in composition and structure the two immiscible melts possess different physical properties. Compared to silicate melt, the ore-forming melt has a lower density and viscosity, which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber. This process is probably responsible for the concentration of ore-forming elements in the upper part of granite bodies and their immediate aureoles. The present experimental results suggest that liquation in felsic magma can be the first step in the ore-forming process during granitoid evolution. |
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